Conductive metal powder connector

ABSTRACT

An electrically conductive metal powder interconnector incorporating a powder bed of submicron diameter nickel/gold particulate powders compacted and contained within a socket and encapsulated by a resilient sealing element. The structure provides a detachably pluggable electrical connector providing a low impedance electrical connection between electrical leads of component elements and other devices to which the elements are attached. Optionally, the structure can function as an interface with connector holes providing the electrical connection between the electrical leads which are located on opposite sides of the interface. Alternatively, the structure can function as a female connector for establishing an electrical contact between the connector and a male pin of a circuit module inserted into the connector.

United States Patent [1 1 Forster et al.

Nov. 6, 1973 CONDUCTIVE METAL POWDER CONNECTOR Inventors: Kenneth R.Forster, Endicott;

Wendell ,1. Wheeler, Endwell, both of N.Y.

International Business Machines Corporation, Armonk, N.Y.

Filed: Dec. 10, 1971 Appl. No.2 206,830

[73] Assignee:

US. Cl. 339/96, 339/278 C Int. Cl l-I0lr 9/08 Field of Search 339/96,118, 278

References Cited UNITED STATES PATENTS 3/1964 Marquis et a1 339/96l1/1956 Mullan 11/1964 Olson et al 339/96 7/1968 Jordan 339/118 R OTHERPUBLICATIONS IBM Technical Bulletin, l'lorchos, Test Socket,

U 339/118 R tematively, the structure can function as a female con-1l./1963, Vol. 6, No. 6, p. 39.

Primary Examiner-Joseph H. McGlynn Attorney-Charles S. Neave et a1.

[5 7] ABSTRACT nector for establishing an electrical contact between theconnector and a male pin of a circuit module inserted into theconnector.

3 Claims, 4 Drawing Figures 1 CONDUCTIVE METAL POWDER CONNECTORBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to electrical connection devices, and more particularly, to afemale connector of the type employing compacted submicron diameternickel/gold particulate powders as a means for estab-' lishing anelectrical contact between the female connector and a male connector tipinserted into the device.

2. Description of the Prior Art In the prior art, numerous resinouscompositions have been made conductive by a physical inter-mixture ofparticles capable of carrying electrical current. These particles havebeen finely divided materials such as, copper, gold, carbon, and thelike. These conductive plastics are empirically produced and theproperties of the conductive mixtures obtained frequently vary from onebatch to another. Such connector devices are generally unreliable.

Various other connector devices comprise a female type connectorsocket-filled with a liquid substance containing metal particles insuspension or other type of conductive fluent material. Such socket typeconnectors are adapted to receive a male connector tip into conductiveengagement with the fluentmaterial'. In these connector devices, theelectrical characteristics vary from one device to the other. i

The present day trend is to the miniaturization andmicro-miniaturization of the electrical circuit equipment which involveshigh density packaging. This trend introduces problems such as providingconsistently reliable electrical interconnecting devices that arepluggably detachable without thc need of heat to effect the connectingand disconnecting operations.

SUMMARY OF THE INVENTION In accordance with the invention, there isprovided electrical connection devices comprising socket carrierreceptacles utilizing submicron diameter nickel/gold particulate powderscompacted to form a powder bed having controlled and predeterminedvolume fraction characteristics.Generally, the connected devicescomprise one or more electrically conductive sockets loded withconductive metal powder and retained therein by an elastomericencapsulating element or membrane. The membrane is bonded to the socketcarrier. The female socket configurations are adapted to receive theprotruding pin elements of a printed circuit card or printed circuitboard, or the like. The compacting or volumetric displacement of thepowder particulate is according to empirically determined standards andthereby produces reliably good electrical interconnections. The hardwarecan be fabricated to provide an interposer type interconnecting deviceenabling printed circuit board to printed circuit board, or printedcircuit card to printed circuit board interconnections. Also, thesockets can be fabricated into printed circuit boards to accept thecircuit module pins for mounting and electrical interconnectionfunctions.

It is a principal object of the invention to provide a novel andimproved electrical connector device which may be employed in a numberof different ways, and which is simple in construction and provides anefficient electrical connection having a low connector. impedancecharacteristic and is capable of meeting present day high speed(nanosecond) signal transmission requirements.

Another object of the invention is to provide an improved femaleelectrical connector device that may be made in very small sizes whichprovides an efficient low impedance electrical connection with apluggably detachable cooperating male connector element.

Another object of the invention is to provide an electricalinterconnection device that is protected from the external environmentalelements.

A still further object of the invention is to provide an improved femaleelectrical connector device which is extremely versatile in itsapplications and which has controllable insertion and withdrawal forcesand makes it especially adaptable for use in muIti-pin connectorarrangements.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of the preferred embodiments of the invention, asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary sectional viewof a socket in a printed circuit board electrical connector constructedin accordance with the present invention;

FIG. 2 is a fragmentary sectional view of an interposer type electricalconnector constructed in accordance with the present invention;

FIG. 3 is the design interconnection geometry for an electricalconnector construction in accordance with the present invention; and

FIG. 4 is a diagrammatic showing of the current paths through a typicalinterposer type electrical connector device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown an improved electrical connector apparatus in accordance with thepresent invention and fabricated as a socket in a printed circuit boardfemale type connector adapted to receive the electrical connecting pinsof a circuit module. The structure comprises a printed circuit board 10having one or more tubular shaped sockets 11. The board 10 is usually ofa dielectric material such as epoxy glass, or the like. The sockets 11are of conductive material such as copper, or gold plated copper, or thelike, and may be formed in the board by conventional electrochemicalprocesses. The sockets 11 are usually electrically interconnected withother circuitry on the board (not shown) and fabricated by conventionaland wellknown printed circuit techniques. The sockets 11 are filled witha conductive submicron diameter size gold plated nickel material powderparticulate and compacted to form the powder bed 12. The powder beds 12are contained in the sockets 11 by means of an elastomeric encapsulatingmembrane 13. The membrane 13 When the module is detached from theprinted circuit board 10, the membrane 13 functions to provided a wipingaction to remove the powder particulates from the surface of the pins14. Preferably, the elastomeric membrane 13 should have a relatively lowcoefficient of sliding friction and provide an easy deformation of theresilient surfaces. The electrical connection'is designed to be fullyseparable.

Referring to FIG. 2, there is a fragmentary showing of an interposer orsocket carrier 20 having sockets 21. The sockets 21 are filled withconductive metal particulate and compacted to form the powder beds 22.The powder beds 22 are retained in the sockets 21 by elastomericencapsulating membranes 23. The membranes 23 are bonded to each side ofthe socket carrier 20. The mating elements are printed circuit cards 24fabricated of dielectric material and support the pins 25 which aresoldered to the printed circuit patterns 26, 27, and 28 that are on theexternal surfaces of the printed circuit cards 24.

The interposer or socket carrier member 20 can be fabricated toaccommodate various area array connector pin configurations. Theencapsulating membranes 23 are adapted to yieldably receive the maletype connector pins 25 of the printed circuit cards 24, the pins beinginsertable through the membranes 23 into the powder beds 22 to establishan electrical connection between the pins 25 and the sockets 21.

The conductivity of the powder beds is contingent upon the volumefraction. The volume fraction may be defined as the ratio of the volumeof the conductive powder to the volume of the spatial region to beoccupied by the powder, defined as:

where V, the total volume of the powder bed m the weight of the powder 8the true density of the powder For the powder submicron nickel/goldparticulate of the preferred embodiment, the true density is determinedas follows:

8 [m(Au)+m(Ni)] m(Ni)/8(Ni)] Alternatively, powder bed compactioncharacteristics are often defined by rheologists in the followingmanner:

a. Fraction solids content,

where:

pb bulk density ps solids density b. Voidage,

0. Porosity 1 (Vo m/S) V and The volume fraction in the range of from 15to 30 percent appears to be an optimum ratio for compacting the powderso as to accept the connector pins in detachably pluggable connection.At lower values of volume fraction compacting the powder scatterincreases rapidly and the powder bed is electrically unstable. At higherlevels of volume fraction compacting it is extremely difficult toforceably insert the male connector pins. Also, the powder bed is notideally suited for detachment operations and repeated male pinpenetration.

FIG. 3 is the design interconnection geometry for an electricalconnector construction in accordance with the present invention, where:

D1 is the connector pin diameter D2 is the socket diameter- Hm is theencapsulating membrane thickness C is the powder bed clearance L is theeffective pin length Hs is the socket length Hb is the printed circuitboard thickness.

The total connector resistance may be expressed as a summation of theprincipal conduction paths; that is, R total R pin socket R powder bedwhere:

R power bed= p powder bed lne l l/D1)/b 21rL ohms where:

p is the resistivity of the respective materials It is the socketthickness lne is the natural logarithm 7 FIG. 4 is an illustration ofthe current flow paths through the interposer type connection. Althoughthe actual conduction path is complex, the principal current flow isradial from the pins to the conductive powder to the plated socketholes. A dual current path exists with the interposer design principlesand the, current flow reverses in the next increment from the platedsocket to the pin via the powder bed.

The following is a general conductance classification of materials:

Metal alloys 9 10" ohm CM Metal powders p 10 to l0" ohm CM Metal filledpolymers p 10* to l0 ohm CM Conductive organics p 10 ohm CM DielectricsThe following is a brief theory summary of the resistance through asphere (submicron metal ball) according to R. Holm, Electric Contacts,4th Edition, Springer-Verlago Resistance through a sphere is as follows:

R (p sphere/1r) ((l/a) l/D) where:

R resistance p resistivity of the sphere a radius of the equipotentialhemispherical surface of the sphere D radius of the sphere Then, thetheory of conduction through powder beds is based on Kirchoffs First Lawwith a statement of the continuity principle stated as:

R: [1/(1/R1)+(1/R2) (1/ ")l for parallel resistor networks.

Now, an expression that furnishes a theoretical description of theconduction mechanism is as follows:

R powder bed WI [ps/21'r (l/a l/D)] where 7 mean number of conductionparticle per chain Fl mean number of conducting chains While theinvention has been particularly shown and described with reference topreferred embodiments thereof, it will be understood by those skilled inthe art that the foregoing and other changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

We claim:

' b. each socket containing a powder bed of conductive metal powderparticulates wherein the powder bed is volume fraction compacted withinthe socket in a range of from -30 percent; and

c. a sealing membrane of resilient deformable material attached to thesocket carrier and overlying the socket opening and being adapted toyieldably receive a male connector pin and admit the connector pin forforcible insertion into the powder bed and conductively engagetherewith.

2. A female electrical connector device as defined in claim 1 whereinthe powder bed is formed of submicron diameter size metal powderparticulates.

3. A female electrical connector device as defined in 10 claim 1 whereinthe powder bed is formed of submicron diameter nickel/gold particulatepowders.

' 2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3r77l'107 Dated November 6, 1973 Inventor) Kenneth R. Forster andWendell J. Wheeler It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

I "I F In the speclflcation, column 4, llnes 15 to 19, the

formula should read as follows:

R total R pin R socket R powder bed Signed and sealed this 23rd day ofApril 1971;.

QSEAL) 'Attest:

EDWARD I-LFLETOHERJRO C. MARSHALL DANN tgttes ting, Officer Commissionerof Patents J

2. A female electrical connector device as defined in claim 1 whereinthe powder bed is formed of submicron diameter size metal powderparticulates.
 3. A female electrical connector device as defined inclaim 1 wherein the powder bed is formed of submicron diameternickel/gold particulate powders.